The primary long-term goal of this work has been to correlate structure-activity relationships for halogenated hydrocarbons and determine how the degree and position of halogenation effects the absorption, disposition and bioaccumulation of these compounds. This work has established that whereas polar halogenated hydrocarbons may be excreted prior to metabolism, simple aryl halides are not excreted prior to metabolism to polar compounds and the rate of metabolism is limited by the availability of adjacent unsubstituted carbon atoms which are thought to facilitate metabolism via arene oxide intermediates. This work has also established that halogenated aromatics are readily absorbed from the gastrointestinal tract, that those compounds which are not polar or are not readily metabolized will persist in the tissues, that chronic exposure to persistent halogenated aromatics will result in bioaccumulation to toxic levels and that the ability to metabolize halogenated aromatics varies widely with species. Studies of halogenated biphenyl transport indicate that these and similar highly lipid soluble compounds are distributed throughout the body in association with hydrophobic sites on blood proteins.